It is the 20 tpi screws that are killing you top speed. Do your
steppers stall before reaching full speed. Most steppers are only
usable to about 1000 rpm before the torque drops off too much. Going
to full steps may not give you any more totrque depending on the type
of drive you are using. Full steps will produce rougher motion and in
general will stall at lower speeds than microstepping. A common set up
is 5 tpi scres with 10th microstep drives. This gives good speed and
resoluion.
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--- In mach1mach2cnc@..., "lhaddix" <lhaddix@i...> wrote:
Hi,
I'm new nad just setting up my motors.
I have a Taig mill with 20tpi leadscrews.
I have 200 step per rev motors (1.8deg)
My stepper drivers currently are set for 1/8 step.
Multiplying this all out means 32000ppi.
I can't get good motion above 5-10 ipm in the
motor tuning dialog with 32000 ppi entered.
When I had the default 2000 ppi entered I got
good motions at what was indicated as 500ipm.
(But was really more like 30ipm since the actual
ppi was 32000)
It dawned on me that the engine can only do 25khz,35khz,45khz.
and that 1/8 stepping is causing the max rate to be limited
by the engine update rate. Is this correct?
If I drop my ppi to 4000 (200ppr * 20 tpi) by changing the
jumpers for full stepping will this raise my max feed and
preserve enough resolution to exceed the
accuracy of the machine by a sufficient amount?
I figure at 4000 ppi if these occur at 25khz this gives
a 375 ipm max feed ceiling set by the mach engine.
(although the motors won't actually be able to do this.)
Is this how you calculate the limit set by the mach update rate?
4000ppi still gives .00025" resolution. Does this exceed the
inherent resolution of the Taig by enough to leave the machine
setting the precision limit and not the steppers?
How much better torque will I get with full stepping?
If I half step for 8000 ppi this would give a 'mach engine limit'
of 187ipm which I believe will still be higher than what the motors
can actually do and give me an 'electrical resolution' of .000125".
How does this tradeoff work? Does all of this sound right or am I
missing something.
